Enable descriptions for statement nodes

[Ana06]

Summary

Enable descriptions for statement nodes such as and and or.

For example:

- or:
  - string: Environment
  - string: windir
  - match: set registry value
description: Modify %windir% environment variable

Motivation

@re-fox has provided a use of case in: mandiant/capa-rules/pull/51

Additional context

We need to come up with a way to render this in the -vv output. Suggestions:

1 - Inline as a comment

- or: # Modify %windir% environment variable
  - string: Environment @ 0x401213
  - string: windir @ 0x40121A

2 - Inline with the already existent description symbol

- or: = Modify %windir% environment variable
  - string: Environment @ 0x401213
  - string: windir @ 0x40121A

3 - Not in line

- or:
  - string: Environment @ 0x401213
  - string: windir @ 0x40121A
description: Modify %windir% environment variable

I like option 2. What do you think? Any other ideas?

This also need to be added in capa explorer.

[williballenthin]

yeah, i'm leaning towards 2 for consistency and keeping a dense representation of the information.

[williballenthin]

we'll need to add support in the json document, too